Study On The Detection Method And Instrument For Rapid Monitoring Pesticides Residues

There are concerns that pesticides used to control pests on food crops are dangerous to people who consume those foods, with the development of people's living conditions and the improvement of people's health consciousness. Pesticide residues in food, water and environment are increasing, leading to the contamination and the poisoning of the environment, animals and human bodies. The poisoning incidences caused by pesticide pollution occurred frequently, millions of people suffered from such acute health problems every year. For the sake of human health protection and environmental control, the detection and control of pesticide residues are of tremendous importance.Pesticide detection is some kind of comprehensive, wide range task. Currently, the methods used to determine organophosphate pesticides (OPs) in fruits and vegetables are mainly based on gas chromatography or high-performance liquid chromatography coupled with various detections, immunoassay, biosensors, portable pesticide detection kit and so on. In this paper, we aim to develop a simple, rapid, inexpensive and sensitive analytical method for routine OPs screening in fruits and vegetables, and try to construct a practical instruments for rapid monitoring of pesticide residues. Biochemistry, nanomaterials and sensing technology are combined to establish novel OPs biosensors modified with nanomaterials. The enzymic reactions and electrochemical characteristics of the biosensors are also discussed; on the other hand, a portable OPs detector is designed and fabricated according to the principle of UV-vis spectrophotometer. The dissertation is divided into two parts including seven chapters. The first part includes the first to the fifth chapter which is the main part in the dissertation. The second part includes the sixth and seventh chapter which is the subordinate part in the dissertation.Chapter one:PrefaceIn this chapter, basic knowledge of pesticide is introduced including the employ and production of pesticide in our country, the sorts of pesticides, the harm caused by pesticide residues etc.. Then, the analytical techniques for OPs detections are presented especially the application of biosensor technology which is revolutionized by the nanotechnology. Finally, the work and significance of this dissertation are brought forward.Chapter two:Au-TiO2/Chit modified sensor for electrochemical detection of trace organophosphate insecticidesIn this paper, Au-TiO2/Chit modified electrode was prepared with Au-TiO2 nanocomposite (Au-TiO2) and Chitosan (Chit) as a conjunct. The Au-TiO2 nanocomposite and the films were characterized by electrochemical and spectroscopy methods. A set of experimental conditions was also optimized for the film's fabrication. The electrochemical and electro-catalytic behaviors of Au-TiO2/Chit modified electrode to trace organophosphates (OPs) insecticides such as parathion were discussed in this work. By differential pulse voltammetry (DPV) measurement, the current responses of Au-TiO2/Chit modified electrode were linear with parathion concentration ranging from 1.0 ng/ml to 7.0×103 ng/ml with the detection limit of 0.5 ng/ml. In order to evaluate the performance of the detection system, we also examined the real samples successfully in this work. It exhibited a sensitive, rapid and easy-to-use method for the fast determination of trace OPs insecticides.Chapter three:Layer-by-Layer self-assembled Acetylcholinesterase/PAMAM-Au on CNT modified electrode for sensing pesticidesIn this paper, an acetylcholinesterase (AChE)/dendrimers polyamidoamine (PAMAM)-Au/Carbon nanotubes (CNTs) multilayer modified electrode based on LbL self-assembled technique was employed in the detection of carbofuran in samples. The configuration of the nanostructure on the electrode provided a favorable environment to the immobilization of AChE. The modified films also improved the electrocatalytic characteristics and electron transfer speed between the films and the surface of electrode. The PAMAM-Au nanoparticles were characterized by SEM and UV-VIS methods. A set of experimental conditions were also optimized for the detection of the pesticides. A linear response over carbofuran concentration in the range of 4.8×10-9M to 0.9×10-7M was exhibited with a detection limit of 4.0×10-9M. The biosensor showed high sensitivity, good stability and reproducibility with promising application.Chapter four:Construction of Tyr/Glu/Fe3O4/Nafion/CNT/GC Biosensor for Detection of PesticideA Tyr/Glu/Fe3O4/Nafion/CNT multilayer modified electrode was employed for the detection of carbofuran in samples. The configuration of the nanostructure on the electrode provides a favorable environment for the Tyr electrocatalytic characterization and fast electron transfer. The surface of the sensor was characterized by TEM methods. A set of experimental conditions were also optimized for the detection of the pesticide.Chapter five:The manufacture of a portable meter for organophosphorus pesticidesA portable meter for the rapid detection of OPs is designed and manufactured based on the inhibition of acetylcholinesterase (AChE). Compared with other existing meters, this one bears a much smaller size which is convenient to carry. A compensated electro-circuit is introduced to the whole circuitry which excludes the influence of light from outside, improving the stability and accuracy of the detector. When applied to the detection of OPs residues in water and vegetable, the meter shows its reliability in result and simplicity in operation.Chapter six:Electrochemical Sensor Prepared from Molecularly Imprinted Polymer for Recognition of 1,3-Dinitrobenzene (DNB)An electrochemical sensor was modified with multi-wall carbon nanotubes (MWCNT) and molecularly imprinted polymer (MIP) material synthesized with acrylamide and ethylene glycol dimethacrylate (EGDMA) in the presence of 1,3-dinitrobenzene (DNB) as the template molecule. The MWCNT and MIP layers were successively modified on the surface of a glassy carbon electrode (GCE), of which the MIP film works as an artificial receptor due to its specific molecular recognition sites. The MIP material was characterized by FT-IR and electrochemical methods of square wave voltammetry (SWV). The interferences of other nitroaromatic compounds (NAC) such as 2,4,6-trinitrotoluene (TNT),1,3,5-trinitrobenzene (TNB) and 2,4-dinitrotoluene (DNT) to DNB were also investigated by the prepared MIP/MWCNT electrode. Compared with other traditional sensors, the MIP/MWCNT modified electrode shows good selectivity and sensitivity. In addition, the current responses to DNB are linear with the concentration ranging from 4.5 X 10-8 mol/L to 8.5×10-6 mol/L with the detection limits of 2.5×10-8 (-0.58 V) and 1.5×10"8 mol/L (-0.69 V) (S/N=3). The construction process of MIP/MWCNT modified electrode was also studied as well. All results indicate that the MIP/MWCNT modified electrode established an improving way for simple, fast and selective analysis of DNB.Chapter seven:{MSU/PDDA}n LBL assembled modified sensor for electrochemical detection of ultratrace explosive nitroaromatic compoundsIn this paper, layer-by-layer{MSU/PDDA}n films assembled by alternate adsorption of mesoporous SiO2 (MSU) and Poly (diallyldimethylammonium chloride) (PDDA) onto a glassy carbon electrode were reported. MSU that we used in this work was synthesized by the precursor of zeolite Y and ionic liquid of 1-hexadecane-3-methylimidazolium bromide (CMIMB), which was used as a template in basic medium. It exhibited larger pore diameter, pore volume and surface area. The electrochemical characteristics of the {MSU/PDDA}n films have been studied by electrochemical impedance spectroscopy in 0.1 M KCl solution containing 5.0 mM Fe(CN)63-/Fe(CN)64-. By differential pulse voltammetry (DPV) measurement, the ultratrace nitroaromatic compounds (NACs) such as TNT, TNB, DNT and DNB can be detected with nM level. The sensitivity for NACs determination in {MSU/PDDA}n films was dependent on the number of layers, pH and ionic strength of electrolyte, based on which a set of optimized conditions for film fabrication was inferred. The current responses were linear with NACs ranging from 10"9 mol/L to 10"7 mol/L with low detection limits. It is a sensitive, rapid and easy-to-use method for the fast determination of NACs.